The present invention relates generally to encoders, and more particularly, to both analog and digital encoder systems and methods for initializing such systems.
The cost of analog encoders increases as the encoder components such as the encoder mask, light element and photo sensors are made more precise and/or with higher tolerances. When working with less expensive encoders the encoder output signals produced have a tendency to be further removed from ideal signals.
U.S. Pat. No. 6,452,512 describes a desirable encoder system having an A/D converter, and a related initialization process in which adjustments to an encoder light element energization level are made, along with adjustments to a dc offset of the signal, in order to produce suitable encoder signals that are within a detection range of the A/D converter.
In one aspect, it would be advantageous to provide an encoder initialization method which can be used to achieve desired encoder signals that are saturated beyond the detection range of an A/D converted or other analog signal detector.
In another aspect, it would be desirable to provide an encoder system and related initialization method that does not require the analog signal levels of an encoder signal to be converted into corresponding digital values, thus saving the cost of an A/D converter.
In one aspect, a method is provided for initializing an encoder system that provides a varying analog output signal to an analog signal detector having a detection range defined by a maximum and a minimum, the encoder system including at least one component that can be controlled to vary at least a peak to peak amplitude of the analog output signal. The method involves the steps of: (a) measuring an output of the analog signal detector while the component is at a first setting; (b) measuring the output of the analog signal detector while the component is at a second setting; and (c) based at least in part upon measurements made in steps (a) and (b), defining an operating setting for the component so as to place an upper envelope of the analog output signal above the maximum of the detection range and a lower envelope of the analog output signal below the minimum of the detection range when the encoder operates with the component at the operating setting.
In another aspect, a method is provided for initializing an encoder system that includes a movable element and produces at least first and second varying analog output signals in response to movement of the movable element, the encoder system including at least one output affecting component that can be adjusted. The method involves the steps of: (a) inputting the first and second analog output signals to an analog to digital converter having a detection range defined by a maximum and a minimum; (b) for each of the first and second analog output signals, measuring a corresponding output of the analog to digital converter while the movable encoder element is moving and the output affecting component is set at at least one known setting; and (c) based at least in part upon the measuring done in step (b), defining an operating setting for the output affecting component so as to place an upper envelope of each of the first and second analog output signals above the maximum of the detection range and the lower envelope of each of the first and second analog output signals below the minimum of the detection range.
In a further aspect, a printer includes the encoder system of the preceding paragraph, and a control unit that carries out the method steps of the preceding paragraph.
In yet another aspect, a method is provided for initializing an encoder system that produces an analog output signal on an output channel, without converting analog signal levels of the analog output signal into corresponding digital values, the system including a light element with an adjustable energization level and the output channel including a photo sensor producing a signal as a function of light received and dc offset circuitry for offsetting the signal to produce the analog output signal. The method involves the steps of: (a) inputting the analog output signal to at least one level detector that detects when the analog output signal increases to an upper threshold level and when the analog output signal decreases to a lower threshold level; (b) while the energization level of the light element is set at a first energization level, adjusting the setting of the de offset circuitry and monitoring for changes in output of the level detector to identify a first offset setting corresponding to the upper threshold level and a second offset setting corresponding to the lower threshold setting; (c) while the energization level of the light element is set at a second energization level, adjusting the setting of the dc offset circuitry and monitoring for changes in output of the level detector to identify a third offset setting corresponding to the upper threshold level and a fourth offset setting corresponding to the lower threshold setting; and (d) based at least in part upon the first, second, third and fourth offset settings identified in steps (b) and (c), establishing an operating energization level for the light element and an operating offset setting for the dc offset circuitry.
In still a further aspect, a method is provided for initializing an encoder system that produces an analog output signal on an output channel, without converting analog signal levels of the analog output signal into corresponding digital values, the system including a light element with an adjustable energization level and the output channel including a photo sensor producing a signal as a function of light received and dc offset circuitry for offsetting the signal to produce the analog output signal. The method involves the steps of: (a) inputting the analog output signal to at least one level detector that detects when the analog output signal increases to an upper threshold level and detects when the analog output signal decreases to a lower threshold level; (b) adjusting the setting of the dc offset circuitry and monitoring for changes in output of the level detector to identify offset settings corresponding to the upper threshold level and the lower threshold level; and (c) based at least in part upon the offset settings identified in step (b), establishing an operating energization level for the light element and an operating offset setting for the dc offset circuitry.
In another aspect, a printer includes an encoder system with a movable element connected for movement with a printer structure, the encoder system including at least one light element and at least first and second output channels, the first output channel producing an analog output signal that varies according to light received by a first photo sensor and the second output channel producing an analog output signal that varies as a function of light received by a second photo sensor. Movement of the movable element varies light received by the first and second photo sensors. A signal detection system includes a first Schmitt trigger connected to receive the analog output signal of the first output channel and having a first upper detection threshold and a first lower detection threshold, with first latching circuitry connected to an output of the first Schmitt trigger for producing (i) a latched output corresponding to the analog output signal of the first output channel reaching the first upper detection threshold and (ii) a latched output corresponding to the analog output signal of the first output channel reaching the first lower detection threshold. The signal detection system further includes a second Schmitt trigger connected to receive the analog output signal of the second output channel and having a second upper detection threshold and a second lower detection threshold, with second latching circuitry connected to an output of the second Schmitt trigger for producing (i) a latched output corresponding to the analog output signal of the second output channel reaching the second upper detection threshold and (ii) a latched output corresponding to the analog output signal of the second output channel reaching the second lower detection threshold.
In a further aspect, a printer includes one of a print head carriage and a paper feed roller connected with an encoder system that produces a varying analog output signal corresponding to movement of the one of the carnage and roller, the encoder system including at least one that can be controlled to vary the analog output signal and a control unit operable to initialize the encoder system to achieve a suitable encoder output signal for use in monitoring movement of the one of the carriage and the roller. A method of triggering an initialization process in the printer involves the steps of: detecting an ambient temperature condition of the printer; and triggering the initialization process if the ambient temperature condition satisfies a certain parameter.